1. Field of the Invention
The present invention relates to an electric motor, and in particular to a terminal unit for connecting leads of stator windings of the electric motor with power cables for supplying electricity from outside.
2. Description of the Related Art
FIG. 12 is a sectional view of an electric motor taken along a central axis Xxe2x80x94X of a rotor shaft 4 of an electric motor for showing an arrangement of a conventional terminal unit mounted on a housing of an electric motor. The electric motor shown in FIG. 12 is a three-phase electric motor for driving a spindle of a machine tool.
In FIG. 12, a housing 1 of the electric motor has a through hole 9 through which leads 7 from windings of respective phases U, V and W of a stator 2 are drawn out of the housing 1. A terminal box 10 having a terminal base 80 formed integrally therewith is mounted on the housing 1. The leads 7 of respective phases drawn through the through hole 9 are led into the terminal box 10, and ends of the leads 7 are respectively connected with conductive plates 81 by means of terminal members 83. In FIG. 12, reference numerals 3, and 5 denote a rotor and a fan for cooling the electric motor, respectively.
FIG. 13 is a top plan view of the terminal unit shown in FIG. 12. The terminal members 83 fixed to ends of the respective leads 7 are connected to the conductive plates 81 on the terminal base 80 by means of screws 82. Terminal member 84 connected with respective ends of the power cables 70 are connected to the conductive plates 81 by means of screws 82. FIG. 13 shows an example of connection of the three leads 7 and the three power cables 70.
As described, in the conventional terminal unit, the terminal base 80 is formed integrally with the terminal box 10 or assembled in the terminal box 10 to have an integral structure. In manufacturing the electric motor, the stator 2, the rotor 3, the cooling fan 5, etc. are manufactured respectively through separate processes and are assembled together in a final assembling process. In the final assembling process, the leads 7 are drawn out of the housing 1 through the through hole 9 and let into the terminal box 10, and then the terminal box 10 is mounted on the housing 1. After the terminal box 10 is mounted on the housing 1, the terminal members 83 of the leads 7 are connected to the conductive plates 81 by rotating the screw 82 manually.
In order to improve an output power specification of the electric motor, a method of obtaining optimum velocity and torque characteristics particularly required for the electric motor has been adopted by switching over connection of windings from a star connection to a delta connection and vice versa. In this case, the three terminal connection have to be changed to six terminal connection for the switch over of the windings. In order to change to the six terminal connection, a size of the terminal base has to be made at least twice as large as the three terminals and also the terminal box has to be made larger, to hinder saving space and saving resources. Since the industry of manufacturing of machine tools, etc. has trended to saving space and saving resources, the conventional arrangement of the terminal unit is counter to the trend.
Particularly, if power cables of large diameters are used for adaptation to a safety standard, radiuses of curvature of the power cables are enlarged to make it difficult to connect them with the power cable connection terminals provided in the terminal box.
As described, connection of the leads with the power cable connection terminals is performed manually. It is not preferable that the manual operations and automatic operations are admixed in an assembling line in view of efficiency and safety, and it has been desired to render all the operations automatic.
The leads are tend to have random orientations since the leads are tend to be bent with their flexibility and it is difficult to fix the position and orientations of the leads. Thus, it is difficult to automatically screw the terminals on the terminal base. Further, in an automatic inspection of the windings of the stator, it is difficult to bring a prove in contact with the leads to make the automatic inspection hardly possible. With the above factors, a full automation of the assembling process of the electric motor has been impeded.
The present invention provides a terminal unit for an electric motor capable of obtaining an output specification of the electric motor by switching the connection of the windings with the same size as the conventional terminal unit, and also improving automation of assembling and inspection process of the electric motor.
According to a first aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at a periphery or in a vicinity of a through hole formed on a housing of the electric motor; a power cable connection terminal arranged at an outer portion of the terminal base, for connection with the power cable; and a lead connector connected with the lead and arranged inner than the power cable connection terminal in a radial direction of the electric motor, and the power cable connection terminal and the lead connector are electrically connected with each other. With the above arrangement, the leads are arranged out of a terminal box and thus the leads are prevented from occupying any substantial space in a terminal box to allow the power cable to occupy a sufficient space in the terminal box.
The leads may be connected with the lead connectors at an inner position of the terminal base in the radial direction of the electric motor and the power cables are to be connected with the power cable connection terminals at an outer position of the terminal base in the radial direction of the electric motor. The leads may be connected with the lead connectors with substantially the same orientation as the lead are drawn out of the housing, and the power cables may be connected with the power cable connection terminals in a plane substantially parallel to an outer surface of the housing.
The terminal base may be positioned above the through hole formed on the housing and at an extremity in a terminal box.
According to a second aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at periphery or in vicinity of a through hole formed on a housing of the electric motor; power cable connection terminals arranged on the terminal base, for connection with the power cables; and lead connectors arranged on the terminal base, each of the lead connectors having a presser portion connected with the lead and a conducting portion formed integrally with the presser portion and connected with the power cable connection terminal.
The power cable connection terminal may comprise a screw terminal, the lead connector has a form of a hook, the leads are connected with the presser portion in the radial direction of the electric motor, and an end part of the conducting portion is fitted to a rod of the screw terminal in an axial direction of the electric motor. The conducting portion may have a female screw and the conducting portion is connected with the power cable connection terminal by an threaded engagement of the screw terminal with the female screw. The presser portion is formed cylindrically with an end closed by a wall and a window is formed at a side of the cylindrical presser portion for confirming an end of the lead.
The lead connector has a linear form, the power cable connection terminal comprises a screw terminal, the leads are connected with the presser portion in the radial direction of the electric motor, and an end part of the conducting portion is fitted to a rod of the screw terminal in the radial direction of the electric motor.
The presser portion may have a cylindrical shape into which the lead is inserted and fixed by caulking, the conducting portion has a wall between the presser portion and an end part connected with the power cable connection terminal, for preventing access of an end of the lead inserted into the presser portion to the end part of the conducting portion by abutting with the end of the lead. The wall may be formed by bending the conducting portion or formed by adding an additional member to the conducting portion. A window may be formed by a gap between an end face of the presser portion and the wall for confirming and end of the lead.
Further, according to a third aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at periphery or in vicinity of a through hole formed on a housing of an electric motor and having lead connector mounting portions; and lead connectors fixed at the lead connector mounting portions of the terminal base, each of the lead connectors having a power cable connection terminal for connection with the power cables, a presser portion for connection with the leads by pressing and a conducting portion for electrically connecting the power cable connection terminal and the presser portion.